Nuclear power reactors are a well known source of energy. In one type of nuclear reactor the nuclear fuel is comprised of elongated rods formed of sealed cladding tubes of suitable material, such as a zirconium alloy, containing uranium oxide and/or plutonium oxide as the nuclear fuel. A number of these fuel rods are grouped together and contained in an open-ended tubular flow channel to form a separately removable fuel assembly or bundle. A sufficient number of these fuel bundles are arranged in a matrix, approximating a right circular cylinder, to form the nuclear reactor core capable of self-sustained a fission reaction. The core is submerged in a fluid, such as light water, which serves both as a coolant and as a neutron moderator.
A typical fuel bundle is formed by an array of fuel rods supported between upper and lower tie plates; the rods typically being in excess of ten feet in length, on the order of one-half inch in diameter and spaced from one another by a fraction of an inch. To provide proper coolant flow past the fuel rods it is important to maintain the rods in precisely controlled, spaced relation such as to prevent bowing and vibration during reactor operation. A plurality of fuel rod spacers are thus utilized at spaced intervals along the length of the fuel bundle for this purpose.
Design considerations of such fuel rod bundle spacers include the following: retention of rod-to-rod spacing; retention of fuel bundle shape; allowance for fuel rod thermal expansion; restriction of fuel rod vibration; ease of fuel bundle assembly; minimization of contact areas between spacer and fuel rods; maintenance of structural integrity of the spacer under normal and abnormal (such as seismic) loads; minimization of reactor coolant flow distortion and restriction; maximization of thermal limits; minimization of parasitic neutron absorption; and minimization of manufacturing costs including adaptation to automated production.
Commonly assigned Matzner et al. U.S. Pat. No. 4,508,679 discloses and claims a nuclear fuel rod bundle spacer uniquely constructed to address these design concerns. As disclosed therein, a spacer is formed of an array of conjoined tubular ferrules surrounded by a peripheral support band, each ferrule thus providing a passage or cell through which a fuel rod or other elongated element of the fuel bundle is inserted. The ferrules are spot welded together and to a peripheral support band to provide an assembly of high structural strength, wherein the thickness of the metal used to form the peripheral support band and ferrules can be minimized to reduce coolant flow resistance and parasitic neutron absorption. Neutron absorption is further decreased by forming the ferrules and peripheral support band of low neutron absorption cross section material.
The rods or elements extending through the ferrules are centered and laterally supported therein between rigid projections and a spring. These rigid projections or stops are formed as fluted or dimpled portions of the ferrule wall at locations near the upper and lower ferrule edges to maximize the axial distance therebetween and thus enhance fuel rod support. The stops are also angularly oriented to minimize projected area and thus disturbance of coolant flow. The formation of these stops in the ferrule sidewall must be accomplished with precision, and their height, as measured from adjacent points on the ferrule peripheral surface to the rod-engaging stop surface, is a critical dimension governing the precise centering of a fuel rod in the ferrule bore. Any eccentricity will adversely effect the uniform distribution of coolant flow through the fuel bundle.
A typical large nuclear reactor core may include on the order of 800 fuel rod bundles, each with as many as seven spacers, and each spacer may comprise sixty fuel rod-positioning ferrules. From this, it is seen that automated, expedited production of these ferrules is of vital importance.
It is accordingly an object of the present invention to provide apparatus for forming surface features in the sidewalls of tubular parts on an automated production line basis.
A further object is to provide forming apparatus of the above-character, wherein the parts are automatically positioned to a requisite orientation prior to forming.
An additional object is to provide forming apparatus of the above-character for creating precision nuclear fuel rod-positioning stops in the sidewalls of ferrules utilized in nuclear fuel bundle spacers.
Another object is to provide forming apparatus of the above-character, wherein the ferrule stops are formed at predetermined plural locations on a multiplicity of spacer ferrules in rapid succession.
Other objects of the invention will in part be obvious and in part appear hereinafter.